Bearing fault detection for surface pumping units

ABSTRACT

Methods and apparatus for operating a rod pumping unit for a wellbore are provided. One example method includes measuring vibration data in the time domain using at least one sensor coupled to a housing for a moving component of the rod pumping unit; converting the vibration data in the time domain to vibration data in the frequency domain; determining that: (1) at least one frequency component of the frequency-domain vibration data in a first frequency band has a power above a first threshold; or (2) a number of frequency components of the frequency-domain vibration data in a second frequency band having power above a second threshold is above a third threshold; and outputting an indication based on the determination.

CLAIM OF PRIORITY UNDER 35 U.S.C. § 119

This application is a continuation of U.S. application Ser. No.15/487,106, entitled “BEARING FAULT DETECTION FOR SURFACE PUMPING UNITS”and filed Apr. 13, 2017, which is assigned to the assignee of thepresent application and hereby expressly incorporated by referenceherein in its entirety.

BACKGROUND OF THE DISCLOSURE Field of the Disclosure

Aspects of the present disclosure generally relate to hydrocarbonproduction using artificial lift and, more particularly, to operating arod pumping unit based on measurements of one or more sensed parametersassociated with the rod pumping unit.

Description of the Related Art

Several artificial lift techniques are currently available to initiateand/or increase hydrocarbon production from drilled wells. Theseartificial lift techniques include rod pumping, plunger lift, gas lift,hydraulic lift, progressing cavity pumping, and electric submersiblepumping, for example.

One common problem with the rod pumping unit is that various movingcomponents of the rod pumping unit may wear down over time, therebyleading to shutdown of the rod pumping unit. Examples of these movingcomponents include bearings and gears.

Thus, there is a need for apparatus and methods of monitoring wear ofmoving components of the rod pumping unit.

SUMMARY OF THE DISCLOSURE

Aspects of the present disclosure generally relate to measuring one ormore parameters associated with a rod pumping unit and taking a courseof action or otherwise operating the rod pumping unit based on themeasured parameters.

Certain aspects of the present disclosure provide a method for operatinga rod pumping unit for a wellbore. The method generally includesmeasuring vibration data in the time domain using at least one sensorcoupled to a housing for a moving component of the rod pumping unit;converting the vibration data in the time domain to vibration data inthe frequency domain; determining that: (1) at least one frequencycomponent of the frequency-domain vibration data in a first frequencyband has a power above a first threshold; or (2) a number of frequencycomponents of the frequency-domain vibration data in a second frequencyband having power above a second threshold is above a third threshold;and outputting an indication based on the determination.

Certain aspects of the present disclosure provide an apparatus formonitoring a moving component in a rod pumping unit for a wellbore. Theapparatus includes at least one sensor configured to measure vibrationdata associated with the moving component in the time domain and atleast one processor electrically coupled to the sensor. The at least oneprocessor is generally configured to convert the vibration data in thetime domain to vibration data in the frequency domain; to determinethat: (1) at least one frequency component of the frequency-domainvibration data in a first frequency band has a power above a firstthreshold; or (2) a number of frequency components of thefrequency-domain vibration data in a second frequency band having powerabove a second threshold is above a third threshold; and to output anindication based on the determination.

Certain aspects of the present disclosure provide a non-transitorycomputer-readable medium for operating a rod pumping unit for awellbore. The medium generally includes instructions executable by oneor more processors to receive vibration data in the time domain from atleast one sensor coupled to a housing for a moving component of the rodpumping unit; to convert the vibration data in the time domain tovibration data in the frequency domain; to determine that: (1) at leastone frequency component of the frequency-domain vibration data in afirst frequency band has a power above a first threshold; or (2) anumber of frequency components of the frequency-domain vibration data ina second frequency band having power above a second threshold is above athird threshold; and output an indication based on the determination.

Certain aspects of the present disclosure provide an apparatus. Theapparatus generally includes means for measuring vibration dataassociated with a moving component in a rod pumping unit in the timedomain; means for converting the vibration data in the time domain tovibration data in the frequency domain; means for determining that: (1)at least one frequency component of the frequency-domain vibration datain a first frequency band has a power above a first threshold; or (2) anumber of frequency components of the frequency-domain vibration data ina second frequency band having power above a second threshold is above athird threshold; and means for outputting an indication based on thedetermination.

Certain aspects of the present disclosure provide a method for operatinga rod pumping unit for a wellbore. The method generally includesmeasuring vibration data in the time domain using at least one sensorcoupled to a housing for a moving component of the rod pumping unit;converting the vibration data in the time domain to vibration data inthe frequency domain; quantifying a life of the moving component basedon the frequency-domain vibration data; and outputting an indicationbased on the quantification.

Certain aspects of the present disclosure provide a non-transitorycomputer-readable medium for operating a rod pumping unit for awellbore. The medium generally includes instructions executable by oneor more processors to receive vibration data in the time domain from atleast one sensor coupled to a housing for a moving component of the rodpumping unit; to convert the vibration data in the time domain tovibration data in the frequency domain; to quantify a life of the movingcomponent based on the frequency-domain vibration data; and to output anindication based on the quantification.

Certain aspects of the present disclosure provide an apparatus formonitoring a moving component in a rod pumping unit for a wellbore. Theapparatus includes at least one sensor configured to measure vibrationdata associated with the moving component in the time domain and atleast one processor electrically coupled to the sensor. The at least oneprocessor is generally configured to convert the vibration data in thetime domain to vibration data in the frequency domain; to quantify alife of the moving component based on the frequency-domain vibrationdata; and top output an indication based on the quantification.

Certain aspects of the present disclosure provide an apparatus. Theapparatus generally includes means for measuring vibration dataassociated with a moving component in a rod pumping unit in the timedomain; means for converting the vibration data in the time domain tovibration data in the frequency domain; means for quantifying a life ofthe moving component based on the frequency-domain vibration data; andmeans for outputting an indication based on the quantification.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description ofthe disclosure, briefly summarized above, may be had by reference toaspects, some of which are illustrated in the appended drawings. It isto be noted, however, that the appended drawings illustrate only typicalaspects of this disclosure and are therefore not to be consideredlimiting of its scope, for the disclosure may admit to other equallyeffective aspects.

FIG. 1 is a schematic depiction of an example rod pumping unit.

FIG. 2 shows an example housing for a sensing device for monitoringbearing wear, in accordance with certain aspects of the presentdisclosure.

FIG. 3 is a block diagram of an example sensing device for monitoringbearing wear, in accordance with certain aspects of the presentdisclosure.

FIG. 4A shows an example frequency spectrum of vibrational amplitudesversus frequency, in accordance with certain aspects of the presentdisclosure.

FIG. 4B shows a threshold amplitude associated with relatively lowerfrequencies on the frequency spectrum of FIG. 4A, in accordance withcertain aspects of the present disclosure.

FIG. 4C shows a frequency range associated with relatively higherfrequencies on the frequency spectrum of FIG. 4A, in accordance withcertain aspects of the present disclosure.

FIG. 5A shows an example frequency spectrum with a window focused onpredetermined values, in accordance with certain aspects of the presentdisclosure.

FIG. 5B shows a resized window for the frequency spectrum of FIG. 5A, inaccordance with certain aspects of the present disclosure.

FIG. 6 is a flow diagram of example operations for a rod pumping unit,in accordance with certain aspects of the present disclosure.

DETAILED DESCRIPTION

Aspects of the present disclosure provide techniques and apparatus formeasuring one or more parameters associated with an artificial liftsystem for hydrocarbon production and operating the system based on themeasured parameters.

FIG. 1 shows an example rod pumping unit 100. The rod pumping unit 100includes a walking beam 110 operatively connected to one or more posts118 via a saddle 147. Attached to one end of the walking beam 110 is ahorse head 125 operatively connected to a polished rod 130. A rod string(not shown) is connected below the polished rod 130 and is connected toa down-hole pump (not shown). The polished rod 130 is axially movableinside the wellhead 160. The walking beam 110 is coupled to a motor 145using a crank arm 132 and gearbox 135, which is described in more detailbelow. The rod pumping unit 100 is operated by a motor control panel 140and powered by the motor 145.

To move the walking beam 110, a pitman arm 120 may be coupled to one endof the walking beam by a tail 146 or equalizer bearing assembly. Forcertain aspects, the rod pumping unit 100 may include two pitman arms120 joined by an equalizer beam. The equalizer beam may be connected tothe walking beam 110 by the bearing assembly. Each pitman arm 120 may bepivotably connected to the crank arm 132 by a crank pin assembly 128,also called a wrist pin. The crank arm 132 may be rotated by a motor 145connected by a belt to a sheave 142, with the gearbox 135 connectedbetween the sheave 142 and the crank arm 132. One or more counterweightblocks 134 may be attached to the crank arm 132.

One common problem with the rod pumping unit 100 is that various movingcomponents of the rod pumping unit 100 may wear down over time, therebyleading to shut down of the rod pumping unit 100. Examples of thesemoving components include gears in the gearbox 135 and bearings locatedin or otherwise associated with the crank pin assembly 128 (e.g., in thewrist pin housing), the tail 146, and the saddle 147.

Aspects of the present disclosure provide methods and apparatus formonitoring the physical condition of at least some of these movingcomponents. The moving components' health may be monitored by measuringvibration experienced by those moving components. In one aspect, the rodpumping unit 100 may include one or more sensors to detect and monitorvibration of moving components of the rod pumping unit 100. For example,the rod pumping unit 100 may include a sensor 171 (e.g., anaccelerometer) to measure the vibration of the bearings in the wrist pinhousing. The sensor 171 may be positioned on the wrist pin cap close tothe wrist pin bearings. Additionally or alternatively, one or more othersensors (not shown) may be positioned at suitable locations on the rodpumping unit 100 to measure the vibration of other components, such asbearings in the tail 146, bearings in the saddle 147, and/or bearings inthe gearbox 135.

In one aspect, the accelerometer is a microelectromechanical system(MEMS)-based accelerometer. The accelerometer may be configured toproduce an electrical signal with an amplitude that is proportional tothe acceleration of the vibrating component to which the accelerometeris attached. The g-force measured by the accelerometer may be monitoredover time to determine vibrational trends in frequencies and amplitudesin the wrist pin bearings. Another example of the sensor 171 formeasuring vibration of the bearings includes acoustic sensors, such asmicrophones or piezoelectric sensors. A certain frequency component, anumber of frequency components in a particular frequency range, and/orthe power of certain frequency components may indicate various levels ofwear in the wrist pin bearings. In this manner, the sensor 171 (andassociated sensor assembly) may be useful in helping prevent furtherdamage to the rod pumping unit 100.

FIG. 2 shows an example housing 200 for a sensor assembly (not shownhere, but depicted in FIG. 3) for monitoring bearing wear, in accordancewith certain aspects of the disclosure. In this aspect, the housing 200is rigid to transmit the vibrations to the sensor 171, as well as toprotect the sensor assembly. The housing 200 includes a location for thesensor 171 and a local power supply. Additionally, the housing 200 mayprovide for attachment to the rod pumping unit 100. The housing 200 maybe configured to attach permanently or temporarily to a location wherethe sensor assembly is able to detect vibrations. For example, thehousing 200 may be magnetically coupled to or bolted onto the wrist pinhousing. The wrist pin housing is a suitable location because thehousing 200 has a direct connection to the wrist pin housing thatpermits any vibrations to be transmitted from the bearings to the wristpin housing, to the housing 200, and to the sensor(s) in the sensorassembly.

The housing 200 may include a lid 201 and a receptacle 204. The sensorassembly may be disposed in and held in place by the receptacle 204. Thelid 201 may be attached to the receptacle 204 via any suitablemechanical coupling method, such as bolts or a threaded connection. Forcertain aspects as illustrated in FIG. 2, the lid 201 may include holesfor bolts 202, such that the lid 201 may be bolted onto the receptacle204. For certain aspects, the housing 200 may be cylindrical, with aheight less than its diameter, and thus, may be referred to as a “hockeypuck.” The sensor assembly may be susceptible to airborne vibrations.Consequently, the housing 200 may also include sound-dampening materialto attenuate this vibrational noise and focus the measuring on thevibrations due to the bearings.

FIG. 3 is a block diagram of a sensor assembly 300 for monitoringbearing wear, in accordance with certain aspects of the disclosure. Thesensor assembly 300 may include at least one processor (e.g., acontroller 302), one or more vibrational sensors 304, ananalog-to-digital converter (ADC) 312, a time-to-frequency-domainconverter 306, and memory 314. The one or more vibrational sensors 304of the sensor assembly 300 may be accelerometers, for example, and inthis case, may be oriented in one, two, three, or more axes (e.g., atriaxial accelerometer). An accelerometer may be used to measure themagnitude of vibrations in the direction of the accelerometer's axis oforientation. For certain aspects, an analog filter (e.g., a low-passfilter, which may also be referred to as an anti-aliasing filter) may beapplied before the ADC 312 in an effort to filter out high frequenciesoutside the frequency band of interest, before these higher frequenciesare aliased into the passband by the act of sampling. For certainaspects, a digital filter (e.g., a low-pass filter or a notch filter)may be applied after the ADC 312 in an effort to remove unwantedfrequencies (e.g., higher frequencies) from the frequency band ofinterest. The digital filter may be implemented with a digital signalprocessor (DSP), which may be a standalone processor or part of anotherprocessor (e.g., the controller 302 or the time-to-frequency-domainconverter 306).

The sensor assembly 300 may have an input/output (I/O) interface 308,which may be configured for wired and/or wireless implementations (e.g.,Bluetooth or WiFi in accordance with IEEE 802.11). The I/O interface 308may have one or more communication ports, antennas, and radio frequency(RF) front-ends for remote communication with a control element, such asthe motor control panel 140, or other processing system. A power supply310 and power management circuitry 311 may provide suitable power forthe sensor assembly 300. The power supply 310 may include a battery.

The time-to-frequency-domain converter 306 may be implemented with adigital signal processor (DSP), which may be a standalone processor orpart of another processor (e.g., the controller 302). Thetime-to-frequency-domain converter 306 may implement a fast Fouriertransform (FFT) or a discrete Fourier transform (DFT), for example, toconvert time-based vibrational data to frequency-based data. The sensorassembly 300 may include memory 314 for storing the frequency-domainvibrational data and/or for storing instructions for the controller 302.For certain aspects, the sensor assembly 300 may also include atemperature sensor 316. In the case of more than one sensor 304, thesensor assembly may include a multiplexer (MUX) 305 configured toselectively route an output of one of the vibrational sensors 304 or theoptional temperature sensor 316 to the ADC 312 for sampling.

For certain aspects, the sensor assembly 300 may be implemented withseparate components (e.g., different integrated circuits (ICs) for thecontroller 302 and the ADC 312), whereas for other aspects, at least aportion of the sensor assembly may be pre-packaged and sold as anoff-the-shelf sensing unit (e.g., a system on a chip (SoC)). Forexample, one suitable off-the-shelf sensing unit is the ADIS16227, adigital triaxial vibration sensor with FFT analysis and storage,available from Analog Devices, Inc. of Norwood, Mass.

Bearing wear may occur due to sand or other foreign objects in a housingcontaining the bearing. As the bearing wears, more room to vibratebecomes available and as vibration increases so too does the amount ofwear. Bearing wear occurs in four levels (also referred to as stages).Each next higher level indicates a greater degree of bearing wear. Eachlevel of bearing wear is associated with certain frequencies (which maybe referred to as “defect frequencies”) that occur due to the vibrationof the bearings. These frequencies can be observed by certain sensors,such as accelerometers. Conventionally, the frequencies of interest forstudying wear of components in various types of pumps have beenrelatively high (e.g., above 8 kHz). However, the frequencies associatedwith bearing wear in a rod pumping unit are significantly lower (e.g.,less than 20 Hz). In fact the lowest frequencies (typically 3 Hz orless) may be representative of the defect frequencies that arecharacteristic of each bearing configuration (e.g., whether in the wristpin housing, the tail, the saddle, or the gearbox of the rod pumpingunit) at different wear levels.

Methods of the present disclosure involve analyzing bearing vibrationaldata in the frequency domain to provide for quantifying the life of abearing in various stages. The first two levels of bearing wear indicatenormal wear and/or minor defects and do not usually signify that thebearings require attention. Level one and level two bearing wear may beidentified by particular characteristics of the frequency-domain bearingvibrational data (e.g., certain defect frequencies or their harmonicsbeing present). For the purposes of a rod pumping unit, critical andnon-critical bearings showing level three wear should most likely bereplaced before reaching level four wear. A bearing showing level threewear has clearly visible defects in the raceways and rolling elements.If the amplitude of certain defect frequencies exceeds a particularthreshold, then it may be assumed that the wear in the bearings isprogressing to a level that may be considered for replacement.Furthermore, harmonics of these defect frequencies may be observed inrelatively higher frequency ranges (e.g., 3 to 8 Hz). The combination of(1) high amplitudes of the lowest (fundamental) frequencies and (2) thepresence and number of the measured harmonics may provide a morereliable means of determining the need for replacement, compared toeither indication taken alone. Additionally, the presence of,proliferation of, and/or amplitude of other non-harmonic frequencies mayalso indicate advanced wear or damage. The windowing (e.g., determinedby threshold amplitudes and frequency ranges) described below provide aconvenient way to characterize level 3 and 4 bearing wear. However, abearing may not be considered as being “worn out” until a combination offrequencies and amplitudes in the frequency spectrum indicates a very“noisy” environment.

FIG. 4A shows an example frequency spectrum 400 of vibrational powerversus frequency collected from two different accelerometers(Accelerometer A and Accelerometer B), in accordance with certainaspects of the disclosure. The vibrational data from the accelerometersmay be converted from time-based data to frequency-based data andplotted to generate the frequency spectrum 400. In the sensor assembly300, for example, the time-to-frequency-domain converter 306 may performthis conversion, as described above.

To determine level three bearing wear in a rod pumping unit or other lowfrequency machinery, a threshold amplitude 403 is shown in FIG. 4B onthe frequency spectrum 400 of FIG. 4A. This threshold amplitude 403 maybe applied to a frequency range 402 of relatively lower frequencies(e.g., less than 6 Hz, less than 4 Hz, or less than 2 Hz) in thefrequency spectrum 400. For example, it may be determined that levelthree bearing wear is demonstrated on the frequency spectrum 400 if anyfrequency components 401 have vibrational amplitudes exceeding 2.0×10⁻⁴g (an example threshold amplitude 403) for frequencies between 0 and 2Hz (an example frequency range 402), as illustrated in FIG. 4B. Thefrequency range 402 and/or threshold amplitude 403 may be stored inmemory (e.g., memory 314) and adjusted by a processor (e.g., thecontroller 302 and/or the time-to-frequency-domain converter 306) in thesensor assembly, during initialization before use or during operation.

Level four wear indicates that the bearing is approaching the end of itslife and needs to be replaced, before failure of the rod pumping unitoccurs. One indicator for level four bearing wear in a rod pumping unitmay manifest as an increase in the quantity of frequency peaks inrelatively higher frequencies (e.g., in frequencies between about 6 Hzand 13 Hz). These higher frequencies may be unrelated to the defectfrequencies that are actually due to the damage that has occurred, orthese frequencies may be harmonics of the fundamental defectfrequencies. The windowing and analysis may include both aspects.

FIG. 4C shows an example frequency range for level four bearing wear onthe frequency spectrum 400 of FIG. 4A, in accordance with certainaspects of the disclosure. One example indicator for level four bearingwear is related to the quantity of frequency components 406 having peaks(e.g., power levels) above a particular threshold 405 in a particularfrequency range 404 (e.g., between frequencies FA and FB inclusive) inthe frequency spectrum. In FIG. 4C, this range of frequencies is about 6to 13 Hz. The quantity of frequency components may also be referred toas “the count” of frequency components above the threshold in thisfrequency range. If the count is determined to exceed a predeterminednumber (another type of threshold), then the bearing wear may bedetermined to be level four. In this case, the sensor assembly mayoutput a control signal or other indication that shuts down the rodpumping unit. This shut-down signal may be transmitted (wirelessly orotherwise) to the motor control panel 140.

In one aspect, the frequency spectrum focuses on a specific range offrequencies and amplitudes that create a window 502. FIG. 5A shows anexample frequency spectrum 500 with a window 502 focused onpredetermined values, in accordance with certain aspects of thedisclosure. The default values for the window 502 may be determinedbased on several parameters of the specific bearing and the particularrod pumping unit, such as the size and type of the bearing or the sizeof the rod pumping unit. The window 502 may be sized to control when athreshold amplitude or a count of frequency components has been exceeded(e.g., either level three or level four thresholds), which may trigger asignal being sent to the pump off controller, an alarm being raised(e.g., sounded), and/or another type of notification occurring. The topedge of the window 502 may set the threshold amplitude in the frequencyspectrum 500. Additionally, filters may be applied in the frequencydomain and configured to exclude or at least attenuate frequenciesoutside of the range of interest (i.e., the sides of the window 502).Filtering the raw signals in this manner may allow focusing on thefrequencies in the range of interest (i.e., inside the window 502),thereby improving analysis.

In another aspect, the window 504 of predetermined frequency andamplitude ranges is customizable and adjustable. FIG. 5B shows thefrequency spectrum 500 of FIG. 5A with a resized window 504, inaccordance with certain aspects of the disclosure. The resized window504 may be resized to adjust when a threshold amplitude or a count offrequency components has been exceeded (e.g., the top edge of the window504), as well as the frequency range of interest (e.g., the sides of thewindow 504), as described above.

Returning to FIG. 3, the sensor assembly 300 may be configured foroperation in a number of different modes, and data may be output fromthe sensor assembly in various ways. For example, the sensor assembly300 may be operated continuously or, in an effort to save power, thesensor assembly may take measurements periodically (e.g., via a power-onand power-off cycle). Furthermore, time-domain and/or frequency-domaindata may be stored in the memory 314 for certain aspects andsubsequently extracted. For other aspects, the time-domain and/orfrequency-domain data may be streamed continuously or sentintermittently. For certain aspects, the data may be transmitted by wireor wirelessly (e.g., via WiFi or Bluetooth) to a computer, for example,for more detailed analysis than that offered by the sensor assembly. Forcertain aspects, wired or wireless communication may occur between thesensor assembly 300 and the motor control panel 140. The sensor assemblymay have a remote connection to a gateway box or control unit, and thegateway box or control unit may have a wired connection to a pump offcontroller. The gateway box or control unit may also indicate whenservice is to be required, trigger an alarm, or have the ability to shutthe pump off. Data from the sensor assembly and/or the computer may becommunicated to the Internet or an intranet, for example, to notifyusers of maintenance or failure issues or to perform analysis.

According to certain aspects, multiple signatures may be identifiedusing one sensor assembly. For example, a sensor assembly placed on thewrist pin cap to measure the wrist pin bearings also has a directconnection to the gearbox. Thus, the sensor assembly placed on the wristpin cap may also measure the vibrations of the gearbox. The sensorassembly may be configured to monitor the status of multiple componentswith identifiable signatures. Furthermore, the sensor assembly may beable to pick up airborne vibrations from nearby sound generators.

FIG. 6 is a flow diagram of example operations 600 for operating a rodpumping unit (e.g., unit 100) for a wellbore, in accordance with certainaspects of the disclosure. Performing the operations 600 may preventdamage to the rod pumping unit. In some cases, performing the operations600 may identify wear of moving components (e.g., bearings) to preventfurther damage to the pumping unit. The operations 600 may be performed,for example, by a sensor assembly (e.g., sensor assembly 300).

The operations 600 may begin, at block 610, by measuring vibration dataof the pumping unit in the time domain. Measuring at block 610 mayinclude using at least one sensor (e.g., sensor 171) coupled to ahousing (e.g., a wrist pin housing, a saddle bearing housing, a tailbearing housing, or a gearbox housing) for a bearing or other movingcomponent. For example, the sensor may include an accelerometerconfigured to measure vibration. The sensor may be coupled to thehousing at a position close to the components (e.g., bearings) ofinterest, such as a wrist pin housing (e.g., crank pin assembly 128), agearbox, a saddle bearing housing, or a tail bearing housing (e.g., anequalizer bearing assembly).

At block 620, the vibration data in the time domain is converted tovibration data in the frequency domain. For example, the time-domainvibration data may be converted to the frequency domain using an FFT ora DFT.

At block 630, it is determined that at least one frequency component(e.g., frequency components 401) of the frequency-domain vibration datain a first frequency band (e.g., frequency range 402) has power above afirst threshold (e.g., threshold amplitude 403) or that a number offrequency components (e.g., frequency components 406) of thefrequency-domain vibration data in a second frequency band (e.g.,frequency range 404) having power above a second threshold (e.g.,threshold 405) is above a third threshold. In cases where the at leastone sensor includes at least one accelerometer, the first and secondthresholds may represent the same or different g-force values. The thirdthreshold may be a positive integer (e.g., representing a thresholdcount of frequency components).

The determination that the at least one frequency component in the firstfrequency band has a power above the first threshold may indicate anonset of excessive wear or mechanical damage to the bearing (e.g., levelthree). The determination that the number of frequency components in thesecond frequency band is above the third threshold may indicateimpending failure of the bearing (e.g., level four).

The second frequency band may have higher frequencies than those in thefirst frequency band. For example, the second frequency band may havefrequencies greater than about 6 Hz (e.g., between 6 Hz and 13 Hz orbetween 8 Hz and 12 Hz), and the first frequency band may havefrequencies less than about 6 Hz, or less than about 3 Hz (e.g., between0 and 1 Hz, or between 0 and 2 Hz).

At block 640, an indication is output based on the determination atblock 630. For example, a frequency component in the first frequencyband had power above the first threshold, and an indication is outputthat the bearing was wearing beyond a suitable amount. For certainaspects, outputting the indication at block 640 includes at least one ofdisplaying a visual indication (e.g., a blinking light-emitting diode(LED) or other light source) or sounding an audible indication (e.g., analarm) for an operator of the rod pumping unit.

According to certain aspects, the operations 600 may further involvecausing the rod pumping unit to cease pumping based on the determinationat block 630 that the number of the frequency components in the secondfrequency band is above the third threshold.

According to certain aspects, the operations 600 may further entailadjusting at least one of the first threshold or a width of the firstfrequency band. The adjusting may be based on at least one of a type ofthe bearing, dimensions of the bearing, or dimensions of the housing.

According to certain aspects, the operations 600 may further includeadjusting at least one of the second threshold, the third threshold, ora width of the second frequency band.

According to certain aspects, the operations 600 may further involvepowering down the at least one sensor after the measuring at block 610for an interval and periodically powering on the at least one sensor toperform at least the measuring again.

According to certain aspects, the operations 600 may further entailwirelessly transmitting at least one of the time-domain or thefrequency-domain vibration data to a processing system.

According to certain aspects, at least the measuring at block 610, theconverting at block 620, and the determining at block 630 are performedby a sensor module (e.g., the sensor assembly 300) coupled to a capattached to the housing.

Certain aspects of the present disclosure provide an apparatus formonitoring a bearing in a rod pumping unit for a wellbore. The apparatusgenerally includes at least one sensor configured to measure vibrationdata in the time domain and at least one processor electrically coupledto the sensor. The least one processor is configured to convert thevibration data in the time domain to vibration data in the frequencydomain; to determine that: (1) at least one frequency component of thefrequency-domain vibration data in a first frequency band has a powerabove a first threshold or (2) a number of frequency components of thefrequency-domain vibration data in a second frequency band having powerabove a second threshold is above a third threshold; and to output anindication based on the determination.

According to certain aspects, the apparatus further includes a housingcontaining the at least one sensor and the at least one processor,wherein the housing is configured to be coupled to another housing forthe bearing in the rod pumping unit.

According to certain aspects, the apparatus further comprises a wirelesstransmitter configured to wirelessly transmit at least one of thetime-domain or the frequency-domain vibration data to a wirelessreceiver.

According to certain aspects, the apparatus further includessound-dampening material configured to attenuate noise signals (e.g.,vibrational signals from sources other than the source(s) of interest)measured by the at least one sensor.

According to certain aspects, the at least one sensor comprises at leastone accelerometer. In this case, the first threshold may represent ag-force value.

According to certain aspects, the apparatus further includes at leastone of a visual indictor or an audible indicator configured to display avisual indication or sound an audible indication, respectively, for anoperator of the rod pumping unit, based on the indication output basedon the determination.

Any of the operations described above, such as the operations 600, maybe included as instructions in a computer-readable medium for executionby the controller 302 or any other suitable processing system. Thecomputer-readable medium may comprise any suitable memory for storinginstructions, such as read-only memory (ROM), random access memory(RAM), flash memory, an electrically erasable programmable ROM (EEPROM),a compact disc ROM (CD-ROM), or a floppy disk.

Certain aspects of the present disclosure provide a non-transitorycomputer-readable medium for operating a rod pumping unit for awellbore. The medium generally includes instructions executable by oneor more processors to: receive vibration data in the time domain from atleast one sensor coupled to a housing for a bearing of the rod pumpingunit; convert the vibration data in the time domain to vibration data inthe frequency domain; determine that: (1) at least one frequencycomponent of the frequency-domain vibration data in a first frequencyband has a power above a first threshold or (2) a number of frequencycomponents of the frequency-domain vibration data in a second frequencyband having power above a second threshold is above a third threshold;and output an indication based on the determination.

Aspects of the present disclosure provide techniques and apparatus formeasuring vibration of a surface rod pumping unit in-situ and analyzingthe measurements to predict the onset of bearing failure. For example,counting the occurrences of peaks above a threshold in a band offrequencies may be used as a criterion for wear or other failureindicators.

While the foregoing is directed to aspects of the present disclosure,other and further aspects of the disclosure may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

The invention claimed is:
 1. A method for operating a rod pumping unitfor a wellbore, comprising: measuring, in the time domain, vibrationdata of a moving component of the rod pumping unit using at least onesensor coupled to a housing for the moving component and disposedadjacent to the moving component; converting the vibration data in thetime domain to vibration data in the frequency domain; determining that:at least one frequency component of the frequency-domain vibration datain a first frequency band has a power above a first threshold; or anumber of frequency components of the frequency-domain vibration data ina second frequency band having power above a second threshold is above athird threshold; and outputting an indication based on the determinationcausing the rod pumping unit to take a course of action to preventfurther damage to the rod pumping unit.
 2. The method of claim 1,wherein the second frequency band comprises higher frequencies relativeto frequencies in the first frequency band.
 3. The method of claim 2,wherein the second frequency band has frequencies greater than about 6Hz and wherein the first frequency band has frequencies less than about6 Hz.
 4. The method of claim 1, wherein: the determination determinesthat the number of frequency components in the second frequency bandhaving power above the second threshold is above the third threshold;and the method further comprises causing the rod pumping unit to ceasepumping based on the determination.
 5. The method of claim 1, furthercomprising adjusting at least one of the first threshold or a width ofthe first frequency band, wherein the adjusting is based on at least oneof a type of the moving component, dimensions of the moving component,or dimensions of the housing.
 6. The method of claim 1, furthercomprising adjusting at least one of the second threshold, the thirdthreshold, or a width of the second frequency band.
 7. The method ofclaim 1, wherein the converting comprises using a fast Fourier transform(FFT).
 8. The method of claim 1, wherein the at least one sensorcomprises at least one accelerometer and wherein the first thresholdrepresents a g-force value.
 9. The method of claim 1, wherein outputtingthe indication comprises at least one of displaying a visual indicationor sounding an audible indication for an operator of the rod pumpingunit.
 10. The method of claim 1, wherein: the moving component comprisesa bearing; the determination that the at least one frequency componentin the first frequency band has a power above the first thresholdindicates an onset of excessive wear or mechanical damage to thebearing; and the determination that the number of frequency componentsin the second frequency band is above the third threshold indicatesimpending failure of the bearing.
 11. The method of claim 1, furthercomprising: periodically powering on the at least one sensor to performat least the measuring; and periodically powering down the at least onesensor after the at least the measuring.
 12. The method of claim 1,further comprising wirelessly transmitting at least one of thetime-domain or the frequency-domain vibration data to a processingsystem.
 13. The method of claim 1, wherein the housing comprises atleast one of a wrist pin housing, a saddle bearing housing, a tailbearing housing, or a gearbox housing.
 14. The method of claim 1,wherein at least the measuring, the converting, and the determining areperformed by a sensor module coupled to a cap attached to the housing.15. An apparatus for monitoring a moving component of a rod pumping unitfor a wellbore, comprising: at least one sensor configured to measure,in the time domain, vibration data of the moving component, the at leastone sensor being coupled to a housing for the moving component and beingdisposed adjacent to the moving component; and at least one processorelectrically coupled to the sensor and configured to: convert thevibration data in the time domain to vibration data in the frequencydomain; determine that: at least one frequency component of thefrequency-domain vibration data in a first frequency band has a powerabove a first threshold; or a number of frequency components of thefrequency-domain vibration data in a second frequency band having powerabove a second threshold is above a third threshold; and output anindication based on the determination causing the rod pumping unit totake a course of action to prevent damage or further damage to the rodpumping unit.
 16. The apparatus of claim 15, further comprising anotherhousing containing the at least one sensor and the at least oneprocessor, wherein the other housing is configured to be coupled to thehousing for the moving component of the rod pumping unit.
 17. Theapparatus of claim 15, further comprising a wireless transmitterconfigured to wirelessly transmit at least one of the time-domain or thefrequency-domain vibration data to a wireless receiver.
 18. Theapparatus of claim 15, further comprising sound-dampening materialconfigured to attenuate noise signals measured by the at least onesensor.
 19. The apparatus of claim 15, wherein the at least one sensorcomprises at least one accelerometer and wherein the first thresholdrepresents a g-force value.
 20. The apparatus of claim 15, furthercomprising at least one of a visual indicator or an audible indicatorconfigured to display a visual indication or sound an audible indicationfor an operator of the rod pumping unit.
 21. A non-transitorycomputer-readable medium for operating a rod pumping unit for awellbore, comprising instructions executable by one or more processorsto: receive vibration data in the time domain of a moving component ofthe rod pumping unit from at least one sensor coupled to a housing forthe moving component and disposed adjacent to the moving component;convert the vibration data in the time domain to vibration data in thefrequency domain; determine that: at least one frequency component ofthe frequency-domain vibration data in a first frequency band has apower above a first threshold; or a number of frequency components ofthe frequency-domain vibration data in a second frequency band havingpower above a second threshold is above a third threshold; and output anindication based on the determination causing the rod pumping unit totake a course of action to prevent damage or further damage to the rodpumping unit.